Catalytic polymerization of polymers containing electrophiic linkages using nucleophilic reagents

ABSTRACT

The disclosure relates to methods and materials useful for polymerizing a monomer. In one embodiment, for example, the disclosure provides a method for polymerizing a monomer containing a plurality of electrophilic groups, wherein the method comprises contacting the monomer with a nucleophilic reagent in the presence of a guanidine-containing catalyst. The methods and materials of the disclosure find utility, for example, in the field of materials science.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/496,535, filed on Jul. 1, 2009, which is incorporated in its entiretyherein.

ACKNOWLEDGEMENT OF GOVERNMENT SUPPORT

This invention was made with Government support under Grant No. NFS-CHE0645891 awarded from the United States National Science Foundation;accordingly, the United States Government has certain rights to thisinvention.

TECHNICAL FIELD

This invention relates generally to the polymerization of monomers, and,more particularly relates to an organocatalytic method for polymerizingmonomers. The invention is applicable in numerous fields, includingindustrial chemistry and manufacturing processes requiring a simple andconvenient method for the preparation of polymers.

BACKGROUND OF THE INVENTION

Polymers containing heteroatoms along the backbone play anever-increasingly important role in modern society, and the variety ofsuch polymers continues to expand at a high rate. For example,poly(ethylene terephthalate) (i.e.,poly(oxy-1,2-ethanediyl-oxycarbonyl-1,4-diphenylenecarbonyl), or “PET”)is a widely used engineering thermoplastic for carpeting, clothing, tirecords, soda bottles and other containers, film, automotive applications,electronics, displays, etc. The worldwide production of PET has beengrowing at an annual rate of 10% per year, and with the increase in usein electronic and automotive applications, this rate is expected toincrease significantly to 15% per year.

Polymers with heteroatoms along the backbone are commonly prepared usingan addition-type polymerization mechanism, in which monomers react toform dimers, which can in turn react with other dimers to formtetramers. This growth process is allowed to continue until polymerswith the desired molecular weight are formed. Unfortunately (and unlikethe alternative chain-growth polymerization mechanism), obtaining highmolecular weight polymer using this mechanism requires carrying thepolymerization reaction to very high conversion.

A frequently-used method for commercial synthesis of (PET) involves atwo-step transesterification process from dimethyl teraphthalate (DMT)and excess ethylene glycol (EO) in the presence of a metal alkanoates oracetates of calcium, zinc, manganese, titanium, etc. This first stepgenerates bis(hydroxy ethylene) teraphthalate (BHET) with theelimination of methanol and the excess EO. The BHET is heated, generallyin the presence of a transesterification catalyst, to generate highpolymer. This process is generally accomplished in a vented extruder toremove the polycondensate (EO) and generate the desired thermoformedobject from a low viscosity precursor.

Some polycondensation reactions, such as the commercial method ofsynthesis of PET described above, require polymerization catalysts. Suchcatalysts may be difficult to prepare, may be unstable to long-termstorage, or may require stringent reaction conditions to providepolymer. Moreover, these catalysts are immortal, limiting theversatility of the widely used mechanical recycling, because at hightemperatures the residual catalyst causes molecular weight degradation.This limits the use of these recycled products to secondary applications(i.e., carpet, playground equipment etc.).

SUMMARY OF THE INVENTION

Accordingly, there is a need in the art for improved polymerizationmethods that involve mild reaction conditions, non-metallic and stablecatalysts, and minimal potentially problematic by-products, whileallowing for the synthesis of polymers with controlled molecularweights, low polydispersities, and/or controlled architecture (e.g.,end-functionalized, branched, block copolymers, etc.).

The invention provides an efficient catalytic polymerization reactionthat does not employ a metallic catalyst. Because a nonmetallic catalystis employed, the polymerization products, in a preferred embodiment, aresubstantially free of metal contaminants. Furthermore, in preferredembodiments, the catalysts are substantially more stable than previousnon-metallic catalysts.

In some embodiments, then, the disclosure provides a method for forminga polymer. The method comprises contacting a monomer with a nucleophilicreagent in the presence of a guanidine-containing compound to form aprepolymer. The method further comprises polymerizing the prepolymer toform a polymer. The monomer comprises at least one electrophilic moiety,and in some embodiments, the monomer comprises two electrophilicmoieties separated by a linker.

In further embodiments, the disclosure provides a composition comprisinga monomer, a nucleophile, and a guanidine-containing compound. Themonomer comprises two electrophilic moieties separated by a linker.

In still further embodiments, the disclosure provides an improved methodfor polymerizing a monomer having at least one electrophilic moiety. Theimprovement comprises contacting the monomer with a nucleophile in thepresence of a guanidine-containing compound.

Preferred catalysts herein are guanidine compounds. In some embodiments,cyclic guanidines, including monocyclic and polycyclic guanidines areused. Polycyclic guanidines suitable for the methods of the disclosureinclude fused and non-fused polycyclic compounds. Further details ofsuitable guanidine catalysts are provided below.

Additional aspects and embodiments of the invention will be provided,without limitation, in the detailed description of the invention that isset forth below.

DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise indicated, this invention is not limited to specificpolymers, catalysts, nucleophilic reagents, or depolymerizationconditions. The terminology used herein is for the purpose of describingparticular embodiments only and is not intended to be limiting.

As used in the specification and the appended claims, the singular forms“a,” “an,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a polymer”encompasses a combination or mixture of different polymers as well as asingle polymer, reference to “a catalyst” encompasses both a singlecatalyst as well as two or more catalysts used in combination, and thelike.

In this specification and in the claims that follow, reference will bemade to a number of terms, which shall be defined to have the followingmeanings:

As used herein, the phrase “having the formula” or “having thestructure” is not intended to be limiting and is used in the same waythat the term “comprising” is commonly used.

The term “alkyl” as used herein refers to a linear, branched, or cyclicsaturated hydrocarbon group (i.e., a mono-radical) typically althoughnot necessarily containing 1 to about 24 carbon atoms, such as methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, octyl, decyl,and the like, as well as cycloalkyl groups such as cyclopentyl,cyclohexyl and the like. Generally, although not necessarily, alkylgroups herein may contain 1 to about 18 carbon atoms, and such groupsmay contain 1 to about 12 carbon atoms. The term “lower alkyl” intendsan alkyl group of 1 to 6 carbon atoms. “Substituted alkyl” refers toalkyl substituted with one or more substituent groups, and this includesinstances wherein two hydrogen atoms from the same carbon atom in analkyl substituent are replaced, such as in a carbonyl group (i.e., asubstituted alkyl group may include a—C(═O)-moiety). The terms“heteroatom-containing alkyl” and “heteroalkyl” refer to an alkylsubstituent in which at least one carbon atom is replaced with aheteroatom, as described in further detail infra. If not otherwiseindicated, the terms “alkyl” and “lower alkyl” include linear, branched,cyclic, unsubstituted, substituted, and/or heteroatom-containing alkylor lower alkyl, respectively.

The term “alkenyl” as used herein refers to a linear, branched or cyclichydrocarbon group of 2 to about 24 carbon atoms containing at least onedouble bond, such as ethenyl, n-propenyl, isopropenyl, n-butenyl,isobutenyl, octenyl, decenyl, tetradecenyl, hexadecenyl, eicosenyl,tetracosenyl, and the like. Generally, although again not necessarily,alkenyl groups herein may contain 2 to about 18 carbon atoms, and forexample may contain 2 to 12 carbon atoms. The term “lower alkenyl”intends an alkenyl group of 2 to 6 carbon atoms. The term “substitutedalkenyl” refers to alkenyl substituted with one or more substituentgroups, and the terms “heteroatom-containing alkenyl” and“heteroalkenyl” refer to alkenyl in which at least one carbon atom isreplaced with a heteroatom. If not otherwise indicated, the terms“alkenyl” and “lower alkenyl” include linear, branched, cyclic,unsubstituted, substituted, and/or heteroatom-containing alkenyl andlower alkenyl, respectively.

The term “alkynyl” as used herein refers to a linear or branchedhydrocarbon group of 2 to 24 carbon atoms containing at least one triplebond, such as ethynyl, n-propynyl, and the like. Generally, althoughagain not necessarily, alkynyl groups herein may contain 2 to about 18carbon atoms, and such groups may further contain 2 to 12 carbon atoms.The term “lower alkynyl” intends an alkynyl group of 2 to 6 carbonatoms. The term “substituted alkynyl” refers to alkynyl substituted withone or more substituent groups, and the terms “heteroatom-containingalkynyl” and “heteroalkynyl” refer to alkynyl in which at least onecarbon atom is replaced with a heteroatom. If not otherwise indicated,the terms “alkynyl” and “lower alkynyl” include linear, branched,unsubstituted, substituted, and/or heteroatom-containing alkynyl andlower alkynyl, respectively.

The term “alkoxy” as used herein intends an alkyl group bound through asingle, terminal ether linkage; that is, an “alkoxy” group may berepresented as —O-alkyl where alkyl is as defined above. A “loweralkoxy” group intends an alkoxy group containing 1 to 6 carbon atoms,and includes, for example, methoxy, ethoxy, n-propoxy, isopropoxy,t-butyloxy, etc. Substituents identified as “C₁-C₆ alkoxy” or “loweralkoxy” herein may, for example, may contain 1 to 3 carbon atoms, and asa further example, such substituents may contain 1 or 2 carbon atoms(i.e., methoxy and ethoxy). The term “alkylthio” as used herein refersto a group —S-alkyl, where “alkyl” is as defined above.

The term “aryl” as used herein, and unless otherwise specified, refersto an aromatic substituent generally, although not necessarily,containing 5 to 30 carbon atoms and containing a single aromatic ring ormultiple aromatic rings that are fused together, directly linked, orindirectly linked (such that the different aromatic rings are bound to acommon group such as a methylene or ethylene moiety). Aryl groups may,for example, contain 5 to 20 carbon atoms, and as a further example,aryl groups may contain 5 to 12 carbon atoms. For example, aryl groupsmay contain one aromatic ring or two or more fused or linked aromaticrings (i.e., biaryl, aryl-substituted aryl, etc.). Examples includephenyl, naphthyl, biphenyl, diphenylether, diphenylamine, benzophenone,and the like. “Substituted aryl” refers to an aryl moiety substitutedwith one or more substituent groups, and the terms“heteroatom-containing aryl” and “heteroaryl” refer to aryl substituent,in which at least one carbon atom is replaced with a heteroatom, as willbe described in further detail infra. If not otherwise indicated, theterm “aryl” includes unsubstituted, substituted, and/orheteroatom-containing aromatic substituents.

The term “aralkyl” refers to an alkyl group with an aryl substituent,and the term “alkaryl” refers to an aryl group with an alkylsubstituent, wherein “alkyl” and “aryl” are as defined above. Ingeneral, aralkyl and alkaryl groups herein contain 6 to 30 carbon atoms.Aralkyl and alkaryl groups may, for example, contain 6 to 20 carbonatoms, and as a further example, such groups may contain 6 to 12 carbonatoms.

The term “alkylene” as used herein refers to a di-radical alkyl group.Unless otherwise indicated, such groups include saturated hydrocarbonchains containing from 1 to 24 carbon atoms, which may be substituted orunsubstituted, may contain one or more alicyclic groups, and may beheteroatom-containing “Lower alkylene” refers to alkylene linkagescontaining from 1 to 6 carbon atoms. Examples include, methylene(—CH₂—), ethylene (—CH₂CH₂—), propylene (—CH₂CH₂CH₂—), 2-methylpropylene(—CH₂—CH(CH₃)—CH₂—), hexylene (—(CH₂)₆—) and the like. Similarly, theterms “alkenylene,” “alkynylene,” “arylene,” “aralkylene,” and“alkarylene” as used herein refer to di-radical alkenyl, alkynyl, aryl,aralkyl, and alkaryl groups, respectively. Collectively, these and otherdi-radical groups are referred to herein as “linkers” or “linkergroups.” By the term “functional linker group” or “functional linker” ismeant di-radical moieties that contain one or more functional groupssuch as an oxo (—O—, such as in an ether linkage), amine (—NR—),carbonyl (—C(═O)—), carbonate, and the like.

The term “amino” is used herein to refer to the group—NZ¹Z² wherein Z¹and Z² are hydrogen or nonhydrogen substituents, with nonhydrogensubstituents including, for example, alkyl, aryl, alkenyl, aralkyl, andsubstituted and/or heteroatom-containing variants thereof.

The terms “halo” and “halogen” are used in the conventional sense torefer to a chloro, bromo, fluoro or iodo substituent.

The term “heteroatom-containing” as in a “heteroatom-containing alkylgroup” (also termed a “heteroalkyl” group) or a “heteroatom-containingaryl group” (also termed a “heteroaryl” group) refers to a molecule,linkage or substituent in which one or more carbon atoms are replacedwith an atom other than carbon, e.g., nitrogen, oxygen, sulfur,phosphorus or silicon, typically nitrogen, oxygen or sulfur. Similarly,the term “heteroalkyl” refers to an alkyl substituent that isheteroatom-containing, the term “heterocyclic” refers to a cyclicsubstituent that is heteroatom-containing, the terms “heteroaryl” and“heteroaromatic” respectively refer to “aryl” and “aromatic”substituents that are heteroatom-containing, and the like. Examples ofheteroalkyl groups include alkoxyaryl, alkylsulfanyl-substituted alkyl,N-alkylated amino alkyl, and the like. Examples of heteroarylsubstituents include pyrrolyl, pyrrolidinyl, pyridinyl, quinolinyl,indolyl, furyl, pyrimidinyl, imidazolyl, 1,2,4-triazolyl, tetrazolyl,etc., and examples of heteroatom-containing alicyclic groups arepyrrolidino, morpholino, piperazino, piperidino, tetrahydrofuranyl, etc.

“Hydrocarbyl” refers to univalent hydrocarbyl radicals containing 1 toabout 30 carbon atoms, including 1 to about 24 carbon atoms, furtherincluding 1 to about 18 carbon atoms, and further including about 1 to12 carbon atoms, including linear, branched, cyclic, saturated andunsaturated species, such as alkyl groups, alkenyl groups, aryl groups,and the like. “Substituted hydrocarbyl” refers to hydrocarbylsubstituted with one or more substituent groups, and the term“heteroatom-containing hydrocarbyl” refers to hydrocarbyl in which atleast one carbon atom is replaced with a heteroatom. Unless otherwiseindicated, the term “hydrocarbyl” is to be interpreted as includingsubstituted and/or heteroatom-containing hydrocarbyl moieties. The term“hydrocarbylene” refers to a di-radical hydrocarbyl group.

By “substituted” as in “substituted hydrocarbyl,” “substituted alkyl,”“substituted aryl,” and the like, as alluded to in some of theaforementioned definitions, is meant that in the hydrocarbyl, alkyl,aryl, or other moiety, at least one hydrogen atom bound to a carbon (orother) atom is replaced with one or more non-hydrogen substituents.Examples of such substituents include, without limitation: functionalgroups such as halo, hydroxyl, sulfhydryl, C₁-C₂₄ alkoxy, C₂-C₂₄alkenyloxy, C₂-C₂₄ alkynyloxy, C₅-C₂₀ aryloxy, acyl (including C₂-C²⁴alkylcarbonyl (—CO-alkyl) and C₆-C₂₀ arylcarbonyl (—CO-aryl)), acyloxy(—O-acyl), C₂-C₂₄ alkoxycarbonyl (—(CO)—O-alkyl), C₆-C₂₀ aryloxycarbonyl(—(CO)—O-aryl), halocarbonyl (—CO)—X where X is halo), C₂-C₂₄alkylcarbonato (—O—(CO)—O-alkyl), C₆-C₂₀ arylcarbonato (—O—(CO)—O-aryl),carboxy (—COOH), carboxylato (—COO⁻), carbamoyl (—(CO)—NH₂),mono-substituted C₁-C₂₄ alkylcarbamoyl (—(CO)—NH(C₁-C₂₄ alkyl)),di-substituted alkylcarbamoyl (—(CO)—N(C₁-C₂₄ alkyl)₂), mono-substitutedarylcarbamoyl (—(CO)—NH-aryl), thiocarbamoyl (—(CS)—NH₂), carbamido(—NH—(CO)—NH₂), cyano (—C≡N), isocyano (—N≡C⁻), cyanato (—O—C≡N),isocyanato (—O—N⁺≡C⁻), isothiocyanato (—S—C≡N), azido (—N═N⁺═N⁻), formyl(—(CO)—H), thioformyl (—(CS)—H), amino (—NH₂), mono- and di-(C₁-C₂₄alkyl)-substituted amino, mono- and di-(C₅-C₂₀ aryl)-substituted amino,C₂-C₂₄ alkylamido (—NH—(CO)-alkyl), C₅-C₂₀ arylamido (—NH—(CO)-aryl),imino (—CR═NH where R=hydrogen, C₁-C₂₄ alkyl, C₅-C₂₀ aryl, C₆-C₂₀alkaryl, C₆-C₂₀ aralkyl, etc.), alkylimino (—CR═N(alkyl), whereR=hydrogen, alkyl, aryl, alkaryl, etc.), arylimino (—CR═N(aryl), whereR=hydrogen, alkyl, aryl, alkaryl, etc.), nitro (—NO₂), nitroso (—NO),sulfo (—SO₂—OH), sulfonato (—SO₂—O⁻), C₁-C₂₄ alkylsulfanyl (—S-alkyl;also termed “alkylthio”), arylsulfanyl (—S-aryl; also termed“arylthio”), C₁-C₂₄ alkylsulfinyl (—(SO)-alkyl), C₅-C₂₀ arylsulfonyl(—(SO)-aryl), C₁-C₂₄ alkylsulfonyl (—SO₂-alkyl), C₅-C₂₀ arylsulfonyl(—SO₂-aryl), phosphono (—P(O)(OH)₂), phosphonato (—P(O)(O⁻)₂),phosphinato (—P(O)(O⁻)), phospho (—PO₂), and phosphino (—PH₂), mono- anddi-(C₁-C₂₄ alkyl)-substituted phosphino, mono- and di-(C₅-C₂₀aryl)-substituted phosphino; and the hydrocarbyl moieties C₁-C₂₄ alkyl(including C₁-C₁₈ alkyl, further including C₁-C₁₂ alkyl, and furtherincluding C₁-C₆ alkyl), C₂-C₂₄ alkenyl (including C₂-C₁₈ alkenyl,further including C₂-C₁₂ alkenyl, and further including C₂-C₆ alkenyl),C₂-C₂₄ alkynyl (including C₂-C₁₈ alkynyl, further including C₂-C₁₂alkynyl, and further including C₂-C₆ alkynyl), C₅-C₃₀ aryl (includingC₅-C₂₀ aryl, and further including C₅-C₁₂ aryl), and C₆-C₃₀ aralkyl(including C₆-C₂₀ aralkyl, and further including C₆-C₁₂ aralkyl). Inaddition, the aforementioned functional groups may, if a particulargroup permits, be further substituted with one or more additionalfunctional groups or with one or more hydrocarbyl moieties such as thosespecifically enumerated above. Analogously, the above-mentionedhydrocarbyl moieties may be further substituted with one or morefunctional groups or additional hydrocarbyl moieties such as thosespecifically enumerated.

In addition, the aforementioned functional groups may, if a particulargroup permits, be further substituted with one or more additionalfunctional groups or with one or more hydrocarbyl moieties such as thosespecifically enumerated above. Analogously, the above-mentionedhydrocarbyl moieties may be further substituted with one or morefunctional groups or additional hydrocarbyl moieties such as thosespecifically enumerated.

When the term “substituted” appears prior to a list of possiblesubstituted groups, it is intended that the term apply to every memberof that group. For example, the phrase “substituted alkyl and aryl” isto be interpreted as “substituted alkyl and substituted aryl.”

Unless otherwise specified, reference to an atom is meant to includeisotopes of that atom. For example, reference to H is meant to include¹H, ²H (i.e., D) and ³H (i.e., T), and reference to C is meant toinclude ¹²C and all isotopes of carbon (such as ¹³C).

By “substantially free of” a particular type of chemical compound ismeant that a composition or product contains less 10 wt % of thatchemical compound, for example less than 5 wt %, or less than 1 wt %, orless than 0.1 wt %, or less than 0.01 wt %, or less than 0.001 wt %. Forinstance, the polymerization product herein is “substantially free of”metal contaminants, including metals per se, metal salts, metalliccomplexes, metal alloys, and organometallic compounds.

Unless otherwise specified, the terms “guanidine compound,” “guanidinecatalyst,” “guanidine-containing compound,” and the like refer tocompounds containing a guanidinyl moiety, i.e., compounds containing thestructure

Accordingly, the invention features a method for preparing a polymerhaving a backbone containing electrophilic linkages. The electrophiliclinkages may be, for example, ester linkages (—(CO)—O—), carbonatelinkages (—O—(CO)—O)—, urethane linkages (—O—(CO)-—NH), substitutedurethane linkages (—O—(CO)—NR—, where R is a nonhydrogen substituentsuch as alkyl, aryl, alkaryl, or the like), amido linkages (—(CO)—NH—),substituted amido linkages (—(CO)—NR— where R is as defined previously),thioester linkages (—(CO)—S—), sulfonic ester linkages (—S(O)₂—O—),ketone linkages (—C(═O)—), and the like. Other electrophilic linkageswill be known to those of ordinary skill in the art of organic chemistryand polymer science and/or can be readily found by reference to thepertinent texts and literature.

In some embodiments, the monomer comprises two electrophilic moietiesseparated by a linker moiety, and has the structure X¹-L-X², wherein X¹and X² are independently electrophilic moieties and L is the linkermoiety. In some embodiments, L is selected from C₁-C₃₀ hydrocarbyleneand functional linker groups. In some embodiments, L is C₁-C₃₀hydrocarbylene. For example, L is selected from C₁-C₃₀ alkylene, C₂-C₃₀alkenylene, C₂-C₃₀ alkynylene, C₅-C₃₀ arylene, and combinations thereof(such as C₁-C₃₀ alkylene linked with a C₅-C₃₀ arylene), wherein any ofthese groups may contain one or more heteroatoms and one or moresubstituents. Linker moieties may also be functional groups, such asheteroatom groups, including thioether (—S—), ether (—O—), and amino(—NR—) groups. In some embodiments, L is substituted or unsubstitutedphenylene (1,4-, 1,3-, or 1,2-connectivity), or substituted orunsubstituted lower alkylene (e.g., methylene, ethylene, propylene,butylene, pentylene, hexylene, septylene, or octylene, including cyclicversions of such linkers).

In some embodiments, X¹ and X² are independently selected from estermoieties (—(CO)—O—R, wherein R is lower alkyl or the like), carboxylicacid or carbonic acid (—COOH or —OCOOH), carbonate moieties(—O—(CO)—O—R, wherein R is lower alkyl or the like), urethane moieties(—O—(CO)—NH—R, wherein R is H, lower alkyl, or the like), substitutedurethane moieties (—O—(CO)—NR′—R, where R′ is a nonhydrogen substituentsuch as alkyl, aryl, alkaryl, or the like), amido moieties (—(CO)—NH—R,wherein R is H, lower alkyl, or the like), substituted amido moieties(—(CO)—NR′—R where R′ is as defined previously), thioester moieties(—(CO)—S—R, wherein R is H, lower alkyl, or the like), sulfonic estermoieties (—S(O)₂—O—R, wherein R is H, lower alkyl, or the like), and thelike. For example, X¹ and X² are lower alkyl esters (e.g., methyl estersor ethyl esters) or amine groups.

Examples of polymers that can be prepared using the methodology of theinvention include, without limitation: poly(alkylene terephthalates)such as poly(ethylene terephthalate) (PET), fiber-grade PET (ahomopolymer made from monoethylene glycol and terephthalic acid),bottle-grade PET (a copolymer made based on monoethylene glycol,terephthalic acid, and other comonomers such as isophthalic acid,cyclohexene dimethanol, etc.), poly(butylene terephthalate) (PBT), andpoly(hexamethylene terephthalate); poly(alkylene adipates) such aspoly(ethylene adipate), poly(1,4-butylene adipate), andpoly(hexamethylene adipate); poly(alkylene suberates) such aspoly(ethylene suberate); poly(alkylene sebacates) such as poly(ethylenesebacate); poly(ε-caprolactone) and poly(β-propiolactone); poly(alkyleneisophthalates) such as poly(ethylene isophthalate); poly(alkylene2,6-naphthalene-dicarboxylates) such as poly(ethylene2,6-naphthalene-dicarboxylate); poly(alkylene sulfonyl-4,4′-dibenzoates)such as poly(ethylene sulfonyl-4,4′-dibenzoate); poly(p-phenylenealkylene dicarboxylates) such as poly(p-phenylene ethylenedicarboxylates); poly(trans-1,4-cyclohexanediyl alkylene dicarboxylates)such as poly(trans-1,4-cyclohexanediyl ethylene dicarboxylate);poly(1,4-cyclohexane-dimethylene alkylene dicarboxylates) such aspoly(1,4-cyclohexane-dimethylene ethylene dicarboxylate);poly([2.2.2]-bicyclooctane-1,4-dimethylene alkylene dicarboxylates) suchas poly([2.2.2]-bicyclooctane-1,4-dimethylene ethylene dicarboxylate);lactic acid polymers and copolymers such as (S)-polylactide,(R,S)-polylactide, poly(tetramethylglycolide), andpoly(lactide-co-glycolide); and polycarbonates of bisphenol A,3,3′-dimethylbisphenol A, 3,3′,5,5′-tetrachlorobisphenol A,3,3′,5,5′-tetramethylbisphenol A; polyamides such as poly(p-phenyleneterephthalamide); poly(alkylene carbonates) such as poly(propylenecarbonate); polyurethanes; and polyurethane/polyester copolymers.

The monomers for polymerization may be obtained from any suitablesource. In one preferred embodiment, the monomers are depolymerizationproducts from recycled post-consumer waste. In another embodiment, themonomers are virgin feedstock.

Polymerization of the monomer is carried out, as indicated herein, inthe presence of a nucleophilic reagent and a catalyst. Nucleophilicreagents are those that comprise one or more nucleophilic groups, suchas hydroxyl, ether, carboxylato (e.g., —COO⁻), amine, azide, sulfhydryl,and the like. Nucleophilic reagents therefore include monohydricalcohols, diols, polyols, amines, diamines, polyamines, sulfhydryls,disulfhydryls, polysulfhydryls, and combinations thereof. Thus, thenucleophilic reagents may contain a single nucleophilic moiety or two ormore nucleophilic moieties, e.g., hydroxyl, sulfhydryl, and/or aminogroups.

In some embodiments, the nucleophilic reagent consists of a singlenucleophilic group, and has the structure R-Nu', wherein R is a C₁-C₃₀hydrocarbyl group and Nu¹ is any nucleophilic group such as thosepreviously described.

In some embodiments, nucleophilic reagents comprise two nucleophilicgroups separated by a linker, and have the structure Nu¹-L¹-Nu², whereinNu¹ is as described previously, Nu² is a nucleophilic group (such asthose described for Nu¹) and wherein L¹ is as described previously forL. Examples of such difunctional nucleophilic reagents include alkyldiols, aryl diols, alkyl diamines, aryl diamines, amino alcohols, aminothiols, and the like.

In some embodiments, the nucleophilic reagent comprises threenucleophilic groups, and has the structure

(also written Nu¹-L³(Nu²)Nu³) wherein Nu¹ and Nu² are as describedpreviously, Nu³ is a nucleophilic group (such as those described forNu¹), and L³ may be any of the linkers described previously for L¹,provided that linker L³ has at least three non-hydrogen substituents(i.e., Nu¹-Nu³). Such nucleophilic reagents allows cross linkingreactions to occur. Any combination of nucleophilic reagents (having thesame or a different number of nucleophilic groups) may be used.

In some embodiments, the nucleophilic reagent will be present in excessof the monomer, meaning that the number of nucleophilic groups exceedsthe number of electrophilic groups at the beginning of the reaction. Insome other embodiments, the ratio of nucleophilic groups toelectrophilic groups is 1:1.

A few specific examples of suitable nucleophilic groups includemethanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol,methylamine, ethylamine, ethylenediamine, propylenediamine,methanethiol, ethanethiol, as well as the following:

Preferred catalysts for the polymerization reactions are organiccompounds containing a guanidine moiety. In some preferred embodiments,the polymerization catalysts are organic guanidines having the structureof formula (I)

wherein R², R³, R⁴ and R⁵ are independently selected from hydrogen andC₁-C₃₀ hydrocarbyl, provided that any two of R², R³, R⁴ and R⁵ may belinked to form a cycle. In preferred embodiments, at least two of R²,R³, R⁴ and R⁵ are linked to form a cycle, such that the compound is acyclic guanidine compound.

For example, R², R³, R⁴ and R⁵ are independently selected fromsubstituted or unsubstituted C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀alkynyl, C₅-C₃₀ aryl, C₆-C₃₀ aralkyl, and C₆-C₃₀ alkaryl, any of whichmay be heteroatom-containing. As mentioned previously, the alkyl,alkenyl, and alkynyl groups include linear, branched, and cyclic suchgroups. The aryl, aralkyl, and alkaryl groups include multicyclic groupssuch as annulated and linked ring systems.

In some embodiments of formula (I), R² and R³ are taken together to forma cycle, and R⁴ and R⁵ are taken together to form a cycle, such that anannulated ring system is formed. Preferred embodiments include compoundshaving the structure of formula (Ia)

wherein

n1 and n2 are independently selected from zero and 1; and

R^(6a), R^(6b), R^(6c), R^(6d), R^(7a), R^(7b), R^(7c), and R^(7d) areindependently selected from H, substituted or unsubstituted C₁-C₃₀alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₅-C₃₀ aryl, C₆-C₃₀ aralkyl, andC₆-C₃₀ alkaryl, any of which may be may be heteroatom-containing,provided that any two of R^(6a), R^(6b), R^(6c), R^(6d), R^(7a), R^(7b),R^(7c), and R^(7d) may be taken together to form a ring.

In some embodiments of formula (Ia), n1 is zero and n2 is 1. In someembodiments of formula (Ia), n2 is zero and n1 is 1. In some embodimentsof formula (Ia), n1 and n2 are both zero. In some embodiments of formula(Ia), n1 and n2 are both 1.

In some embodiments of formula (Ia), one of R^(6a) and R^(6b) is C₅-C₃₀aryl, and the other is Hydrogen, and one of R^(7a) and R^(7b) is C₅-C₃₀aryl, and the other is H. In some such embodiments, the C₅-C₃₀ arylgroup is phenyl.

In some embodiments of formula (Ia), R^(6c), R^(6d), R^(7c), and R^(7d)are each H. Examples of such embodiments include the followingcompounds:

In some embodiments of formula (I), R³ and R⁴ are taken together to forma cycle. For example, preferred embodiments include compounds having thestructure of formula (Ib)

wherein

n3 is selected from 0 and 1;

X¹ and X² are independently selected from —NR¹⁰— and —C(R¹¹)(R¹²)—,wherein R¹⁰, R¹¹, and R¹² are independently selected from H and alkyl;and

R^(8a), R^(8b), R^(9a), and R^(9b) are independently selected fromalkyl, aryl, aralkyl, and alkaryl, provided that any two of R^(8a),R^(8b), R^(9a), R^(9b), R¹⁰, R¹¹, and R¹² may be taken together to forma cycle.

In some embodiments of formula (Ib), R^(9a) and R^(9b) are both H, andX¹ and X² are both —CH₂—, such that the compounds have the structure offormula (Ic)

Further examples of embodiments of formula (Ib) include compounds havingthe structures

In some embodiments of the structures shown above, R² and R⁵ areindependently selected from substituted or unsubstituted C₁-C₃₀ alkyland substituted or unsubstituted heteroatom-containing C₁-C₃₀ alkyl. Forexample, R² and R⁵ may be C₃-C₃₀ alicyclic, such as cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl (Cy), cycloheptyl, or cyclooctyl.Also, for example, R² and R⁵ may be methyl, ethyl, propyl (i-propyl,n-propyl), or butyl (t-butyl, n-butyl, sec-butyl), or may beheteroatom-containing such as 3-dimethylaminopropyl or a salt thereof.

In some embodiments, the guanidine-containing compounds described hereinare chemically more stable than other catalysts capable of causingdepolymerization, such as N-heterocyclic carbene catalysts. In someembodiments, compared with N-heterocyclic carbene catalysts undersimilar conditions, the guanidine-containing compounds decompose at asubstantially lower rate. Preferred catalysts are substantially stableunder some or all of the depolymerization conditions described herein.

The guanidine-containing compounds described herein may be synthesizedby any appropriate method, and such methods are readily ascertainablefrom the relevant literature. For example, cyclic guanidines may beprepared using the methods disclosed in U.S. Pat. No. 4,797,487 entitled“Production of Bicyclic Guanidines from Bis(aminoalkyl)amine.” It willbe appreciated that the handling of certain guanidine-containingcompounds may require precautions to avoid decomposition. For example,mixing of the reaction components may require an inert atmosphere.

The polymerization catalysts of the disclosure (i.e.,guanidine-containing compounds) are typically present in the reactionmixture in an amount (i.e., a “catalyst loading”) that is less than 5mol %, or less than 2 mol %, or less than 1 mol %, or less than 0.5 mol%, or less than 0.1 mol %, with less than 1 mol % being particularlypreferred. Such catalyst loadings are measured as mol % relative to thetotal amount of monomer used in the reaction.

The polymerization reaction occurs by initial formation of a prepolymercomprising the product of a reaction between the monomer andnucleophilic reactant, and subsequent condensation polymerization of theprepolymer. In some embodiments, the prepolymer comprises one or moreelectrophilic groups and one or more nucleophilic groups; for examplethe prepolymer comprises two nucleophilic groups and two electrophilicgroups. In such embodiments, the condensation reaction may occur as theelectrophilic group of one prepolymer molecule reacts with thenucleophilic group of another prepolymer molecule. In embodiments wherethe condensation reaction produces non-polymeric byproducts(particularly small organic molecules such as water, H₂, ethyleneglycol, propylene glycol, etc.), such products may be removed during thereaction to help the polymerization achieve higher molecular weightpolymers.

The initial formation of the prepolymer may be carried out in a suitablesolvent, or without any solvent. The nucleophilic reagent may functionas a solvent. When a separate solvent is used, it is preferable that thesolvent is removed prior to polymerization of the prepolymer. Thus, insome embodiments, the polymerization reaction is started in a solventfor a predetermined period of time, after which time the solvent isremoved (such as by applying reduced pressure and/or increasedtemperature), and the polymerization is allowed to continue for a periodof time sufficient to provide polymer of the desired molecular weight.

The polymerization reaction may be carried out in an inert atmosphere.In carrying out the reactions, combination of the reactants may beaccomplished in any order. For example, the reactants can be combined bydissolving a catalytically effective amount of the selected catalyst ina solvent, combining the monomer and the catalyst solution, and thenadding the nucleophilic reagent. In a particularly preferred embodiment,the monomer, the nucleophilic reagent, and the catalyst are combined anddissolved in a suitable solvent, and polymerization thus occurs in aone-pot, one-step reaction.

The reaction mixture is typically, although not necessarily, agitated(e.g., stirred), and the progress of the reaction can be monitored bystandard techniques, although visual inspection is generally sufficient.Examples of solvents that may be used in the polymerization reactioninclude organic, protic, or aqueous solvents that are inert under thepolymerization conditions, such as aromatic hydrocarbons, chlorinatedhydrocarbons, ethers, aliphatic hydrocarbons, or mixtures thereof.Preferred solvents include toluene, methylene chloride, tetrahydrofuran,methyl t-butyl ether, Isopar, gasoline, and mixtures thereof. Reactiontemperatures are in the range of about 25° C. to about 300° C. The totalpolymerization reaction time will generally, although again notnecessarily, be in the range of about 1 to 24 hours.

In some embodiments, the reactions are carried out by first combiningthe monomer with the nucleophilic reagent and the catalyst in a solvent.After allowing sufficient time for the monomer to react with thenucleophilic reagent to form a prepolymer, the reaction conditions arechanged to encourage polymerization of the prepolymer. For example,elevated temperature and/or reduced pressure may be applied in order toforce the condensation of prepolymer molecules. In some embodiments, thetemperature of the reaction after formation of the prepolymer is raisedto between 100° C. and 200° C., or greater than about 150° C., orgreater than about 170° C. The amount of time required to form theprepolymer from the monomer and the nucleophilic reagent will varydepending upon the reactants and conditions, but may be estimated ordetermined by the usual analytical methods. The temperature duringformation of the prepolymer may be room temperature or higher, forexample between 30° C. and 100° C.

The polymerization product from reactions according to the inventioncontains product polymer and the guanidine-containing catalyst, whichmay be removed from the polymer product in the usual manner.

Because the polymerization catalysts disclosed herein do not containmetals, the methods of the disclosure allow for the polymerization of amonomer starting material to provide a polymerization product that issubstantially free of metal contaminants. In particular, theconcentration of metal contaminants in the polymer products is equal toor less than the concentration of metal contaminants in the startingmaterials prior to polymerization. For example, when a sample ofdimethyl terephthalate (DMT) is polymerized according to the invention,and the sample of DMT has a certain concentration of metal contaminant(e.g., residual metals from any reaction that was used to prepare theDMT, such as a metal catalyst used in a depolymerization reactionrecycling PET into DMT via depolymerization), the polymerizationreaction according to the invention does not increase the totalconcentration of metal contaminants. The polymer products (e.g., PET)contain the same or lower concentration of metal contaminants as thestarting materials. A lower concentration of metal contaminant may beobserved if the polymer products are subjected to any purification steps(such as precipitation, filtration, etc.). As a further example, asample of DMT having no metal contaminants (or an undetectable level ofmetal contaminants) may be polymerized according to the invention toyield polymer products having no metal contaminants (or an undetectablelevel of metal contaminants).

In some embodiments, the polymerization reactions of the disclosureallow preparation of polymer products having a metal contaminantconcentration that is immeasurable or equal to or less than the metalcontaminant concentration of the starting materials used to prepare thepolymer. Such polymer products may have substantially less metalcontaminant concentrations than similar polymers prepared usingconventional (i.e., metal catalyzed) polymerization methods.

For example, depending on the method of manufacture, conventional PETused for drinking bottles may have a residual metal contamination levelof up to 50 ppm, or up to 20 ppm, or up to 5 ppm. In some embodiments,the methods of the invention provide PET suitable for food and beveragestorage since the level of metal contamination of the polymerizationproducts will be no higher than the level of metal contamination of theoriginal monomer. Thus, in some embodiments, the methods of theinvention provide polymers having a metal contamination concentration of≦50 ppm, or ≦20 ppm, or ≦5 ppm, or below 1 ppm.

The methods described herein find utility, for example, in thepreparation of polymers and items made from polymers, the use ofrecycled polymer depolymerization products, and similar areas asdescribed herein throughout.

All patents, patent applications, and publications mentioned herein arehereby incorporated by reference in their entireties. However, where apatent, patent application, or publication containing expressdefinitions is incorporated by reference, those express definitionsshould be understood to apply to the incorporated patent, patentapplication, or publication in which they are found, and not to theremainder of the text of this application, in particular the claims ofthis application.

It is to be understood that while the invention has been described inconjunction with the preferred specific embodiments thereof, that theforegoing description as well as the examples that follow, are intendedto illustrate and not limit the scope of the invention. It will beunderstood by those skilled in the art that various changes may be madeand equivalents may be substituted without departing from the scope ofthe invention, and further that other aspects, advantages andmodifications will be apparent to those skilled in the art to which theinvention pertains.

EXAMPLES Example 1

Sample 1 is a PET that was polymerized (bulk) with 2 mol % of catalystsrelative to DMT. Since the concentration of ethylene glycol tends tovary during the course of the polymerization, all catalysts loadings arerelative to dimethyl terephthalate (DMT). The maximum polymerizationtemperature in the case was 200° C.

DMT (0.5 grams, 0.0025 mol) was added to a round bottom flask togetherwith ethylene glycol (0.62 grams, 0.01 mol). To this slurry, TBD (0.006grams, 0.00005 mol) was added. The reaction was heated to 40° C. undervacuum (3 hours), 100° C. (1 hour) and 200° C. for 3 hours.

Example 2

Sample 2 was also PET that was polymerized with 1.5 mol % catalystrelative to DMT. The maximum polymerization temperature in this case was275° C.

DMT (3.0 grams, 0.015 mole) and ethylene glycol (6.5 grams, 0.01 mol)was added to a round bottom flask together with TBD (0.01 grams,0.000075 mol). The reaction was heated to 40° C. under nitrogen (2hours), heated to 60° C. under vacuum (30 min) and heated to 100° C.(vacuum, 1 hour). The reaction was then heated to 150° C. (vacuum, 35min. where it became homogeneous. The reaction was then heated to 200°C. (1.5 hours) and then 275° C. (1 hour) to finish the reaction.

The product polymers were characterized by ¹H NMR.

Example 3

Combining bis(hydroxy ethylene) terephthalate (BHET) with1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and heating the mixture undervacuum results in the formation of poly(ethylene terephthalate).Polymerization can also be carried out by heating dimethyl terephthalatewith ethylene glycol in the presence of TBD catalysts followed byheating under vacuum. This process is shown in Scheme 1.

Example 4

Synthesis of 1,4,6-triazabicyclo[3.3.0]-oct-4-ene (TBO). With stirringat room temperature under nitrogen atmosphere, xylenes (300 mL),diethylenetriamine (20.6 g, 21.7 mL, 0.2 mol), and carbon disulfide(15.2 g, 12.0 mL, 0.2 mol) were added to a three-necked flask. A whiteprecipitate formed immediately and the suspension was heated to reflux.Evolution of H₂S from the reaction exhaust was monitored using filterpaper soaked in a methanolic suspension of lead(II) acetate. After 10days of reflux under nitrogen, GC/MS analysis confirmed quantitativeconversion to the target compound. Upon cooling to room temperature awhite solid crystallized from solution, and the supernatant wasdecanted. The solid was washed with 2×50 mL portions of acetone andpentane, respectively, and dried under vacuum overnight. (8.65 g, 39%).¹H NMR 400 MHz (CDCl₃).differential. (ppm)=6.02 [br s, 1H, N—H], 3.79[t, 2H, backbone CH₂, J=7.0 Hz], 3.05 [t, 2H, backbone CH₂, J=7.0 Hz].¹³C NMR 100.6 MHz (CDCl₃).differential. (ppm)=171.18 [central sp² C],52.62 [backbone CH₂], 49.38 [backbone CH₂]. LRMS (m/z): 112.1 (positiveion, M+H).

Example 5

Synthesis of Guanidine catalysts. The general procedure is shown inScheme 2.

DCC was reacted neat (110° C.) with a secondary amine. Once the DCCmelted a homogeneous solution was formed and the reaction was allowed toproceed overnight to generate a viscous oil/gel. The reaction wasfollowed by GC/MS and quantitative conversion of starting material wasaccomplished in .about.12 hours. Compounds were purified either bykugelroh distillation or by column chromatography.

Synthesis of Guanidinium 1: Dicyclohexylcarbodiimide (3 g, 14.8 mmol)and pyrrolidine (10 ml, 120 mmol) were heated to reflux overnight underN₂. The excess pyrrolidine was distilled off and the product waspurified by Kugelroh distillation (265° C.) to yield a colorless oil.The product guanidine compound has the structure shown below.

Synthesis of Guanidinium 2: DCC (0.93 g, 4.52 mmol) and TBD (0.66 g,4.76 mmol) were allowed to react for 20 (125° C. under N₂). The gel likeproduct was purified by Kugelroh distillation 265° C. to yield a whitecrystalline solid T_(m)=69-71° C. The product guanidine compound has thestructure shown below.

Synthesis of Guanidinium 3: DCC (0.70 g, 3.39 mmol) and (s)-(−)α,α-diphenyl-2-pyrrolidinemethanol (0.86 g, 3.39 mmol) were heated(under N₂) at 80° C. for 20 h. Temperatures above 100° C. resulted indecomposition. The product was purified using column chromatographs(ethyl acetate/hexane (60/40)) to yield a white crystalline solidT_(m)=104-106° C. The product guanidine compound has the structure shownbelow.

We claim:
 1. A composition comprising a monomer, a nucleophile, and aguanidine-containing compound according to Formula (Ib)

wherein the monomer comprises two electrophilic moieties separated by alinker and further wherein: n3 is selected from 0 and 1; X¹ and X² areindependently selected from the group consisting of —NR¹⁰— and—C(R¹¹)(R¹²)—, wherein R¹⁰, R¹¹, and R¹² are independently selected fromH and alkyl; R² and R⁵ are independently selected from the groupconsisting of substituted and unsubstituted C₁-C₃₀ alkyl; and R^(8a),R^(8b), R^(9a), and R^(9b) are independently selected from the groupconsisting of H and substituted and unsubstituted alkyl, aryl, aralkyl,and alkaryl, any of which may be heteroatom-containing, provided thatany two of R^(8a), R^(8b), R^(9a), R^(9b), R¹⁰, R¹¹, and R¹² may betaken together to form a cycle.
 2. The composition of claim 1, whereinthe guanidine-containing compound has the structure


3. The composition of claim 1, wherein the guanidine-containing compoundis present in an amount effective to cause reaction of the electrophilicmoiety with the nucleophile.
 4. The composition of claim 1, wherein theguanidine-containing compound is present in an amount less than about 1mol % relative to the amount of monomer.
 5. The composition of claim 1,wherein the nucleophile comprises at least one hydroxyl group.
 6. Thecomposition of claim 1, wherein the electrophilic moieties are selectedfrom ester, carbonate, urethane, substituted urethane, phosphate, amido,substituted amido, thioester, sulfonate ester, and combinations thereof.7. The composition of claim 1, wherein the monomer has the structureX¹-L-X², wherein X¹ and X² are electrophilic moieties independentlyselected from esters, carbonates, urethanes, substituted urethanes,phosphates, amido groups, substituted amido groups, thioesters, andsulfonate esters, and L is a linker moiety selected from C₁-C₃₀hydrocarbylene and functional linker groups.
 8. The composition of claim7, wherein X¹ and X² are ester moieties.
 9. The composition of claim 7,wherein L is selected from substituted and unsubstituted C₁-C₂₄alkylene, substituted and unsubstituted C₅-C₂₄ arylene, substituted andunsubstituted C₅-C₂₄ alkarylene, and substituted and unsubstitutedC₅-C₂₄ aralkylene.
 10. A polymer comprising the composition of claim 1,wherein the polymer is selected from the group consisting ofpoly(alkylene terephthalates), poly(alkylene adipates), poly(alkylenesuberates), poly(alkylene sebacates), poly(alkylene isophthalates),poly(alkylene sulfonyl-4,4′-dibenzoates), poly(alkylene2,6-naphthalene-dicarboxylates), poly(p-phenylene alkylenedicarboxylates), poly(trans-1,4-cyclohexanediyl alkylenedicarboxylates), poly(1,4-cyclohexane-dimethylene alkylenedicarboxylates), poly([2.2.2]-bicyclooctane-1,4-dimethylene alkylenedicarboxylates), polycarbonates of bisphenol A, polyamides,poly(alkylene carbonates), lactic acid polymers and copolymers,polyurethanes and polyurethane/polyester copolymers,poly(ε-caprolactone), and poly(β-propiolactone).
 11. A polymercomprising the composition of claim 1, wherein the polymer comprisespoly(ethylene terephthalate) (PET).
 12. A polymer comprising thecomposition of claim 1, wherein the polymer comprises poly(butyleneterephthalate) (PBT).
 13. A polymer comprising the composition of claim1, wherein the polymer comprises poly(hexamethylene terephthalate). 14.A polymer comprising the composition of claim 1, wherein the polymer isselected from the group consisting of poly(ethylene adipate),poly(1,4-butylene adipate), and poly(hexamethylene adipate).
 15. Apolymer comprising the composition of claim 1, wherein the polymer isselected from the group consisting of poly(ethylene suberate),poly(ethylene sebacate), poly(ethylene isophthalate), and poly(ethylenesulfonyl-4,4′-dibenzoate).
 16. A polymer comprising the composition ofclaim 1, wherein the polymer is selected from the group consisting ofpoly(ethylene 2,6-naphthalene-dicarboxylate), poly(p-phenylene ethylenedicarboxylates), poly(trans-1,4-cyclohexanediyl ethylene dicarboxylate),poly(1,4-cyclohexane-dimethylene ethylene dicarboxylate), andpoly([2.2.2]-bicyclooctane-1,4-dimethylene ethylene dicarboxylate). 17.A polymer comprising the composition of claim 1, wherein the polymer isselected from the group consisting of 3,3′-dimethylbisphenol A;3,3′,5,5′-tetrachlorobisphenol A; and 3,3′,5,5′-tetramethylbisphenol A.18. A polymer comprising the composition of claim 1, wherein the polymercomprises poly(p-phenylene terephthalamide).
 19. A polymer comprisingthe composition of claim 1, wherein the polymer comprises polypropylenecarbonate).
 20. A polymer comprising the composition of claim 1, whereinthe polymer is selected from the group consisting of (S)-polylactide,(R,S)-polylactide, poly(tetramethylglycolide), andpoly(lactide-co-glycolide).